Three-stage mast assembly for a lift truck

ABSTRACT

A three-stage mast assembly for a lift truck, consisting of an outer mast channel, an intermediate mast channel and an inner mast channel, all of I- or L-shaped cross section, wherein the forward and rearward flanges, respectively, of the intermediate mast channel are arranged rearwardly from the forward and rearward flanges, respectively, of the outer and inner mast channels.

[ 5] Feb.l,l972

[56] References Cited UNITED STATES PATENTS [54] THREE-STAGE MASTASSEMBLY FOR A LIFT TRUCK d 0 0 w n e e r m 0 m M J mm .L h 5 mm m w Km... n O n N a SK mu n n8 i s .mA 1] 23 77 [i Selsakusho, AichiPrefecture, Japan Feb. 11, 1970 Primary Examiner-Harvey C. HomsbyAttorney-Wenderoth, Lind & Ponack [22] Filed:

211 Appl. No.:

ABSTRACT [30] Foreign Application Priority Data Feb. 25, 1969 Athree-stage mast assembly for a lift truck, consisting of an outer mastchannel, an intermediate mast channel and an [51] Int. [58] Field of 2Claims, 7 Drawing Figures PATENTED FEB H972 SHEET 1 BF 2 FIG.

3 IAZ A 21 a L SHUJI OHTA,

ATTORNEY S PATENTEU FEB 1 I972 SHEEY 2 0F 2 FIG.

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JNVENTOR ATTORNEY THREE-STAGE MAST ASSEMBLY FOR A LIFT TRUCK Thisinvention relates to a three-stage mast assembly for lift truckcomprising three channels, viz an outer mast channel, an intermediatemast channel and an inner mast channel.

An object of this invention is to provide an improved arrangement of themast assembly of the three-stage type, in which the mast assembly has animproved construction, removing the disadvantage inherent in a presentlyknown arrangement of a mast construction of this type. Other objects ofthe invention will become apparent from the following detaileddescription taken in conjunction with the accompanying drawings.

In the accompanying drawings,

FIGS. 1 and 2 are side elevations of the three-stage mast assembly forlift trucks heretofore in use;

FIGS. 3 and 4 are explanatory plan views partly in transverse section ofsaid mast assembly shown in FIGS. 1 and 2 respectively;

FIG. 5 is a side view of the mast assembly according to the presentinvention;

FIG. 6 is an explanatory plan view partly in transverse section of themast assembly of this invention; and

FIG. 7 is a plan view similar to FIG. 6 showing a modified form of thearrangement of the mast assembly of this invention.

Referring to the drawings, FIGS. 1-4 show the arrangement of thethree-stage mast assembly of a type extensively used in lift trucks, theouter mast channel 1, the intermediate mast channel 2 and the inner mastchannel 3 being telescopically associated with each other through mastrollers. The forward and rearward flanges 2A-2B of the intermediate mastchannel 2 being arranged in line with the forward and rearward flangeslA-lB of the outer mast channel 1 as well as with the forward andrearward flanges 3A-3B of the inner mast channel 3, as shown in FIG. 3.In another type (FIG. 4), the forward and rearward flanges 2A-2B arearranged in the position slightly offset from the forward and rearwardflanges lA-lB of the outer mast channel 1 and from the forward andrearward flanges 3A-3B of the inner mast channel 3. In the firstexample, the intermediate and inner mast guide rollers 14, 15, I6 and 17which are in engagement with the adjacent masts receive a moment in thefore and aft direction, and more than two guide rollers will have to beprovided within the range of overlap formed at the uppermost position ofthe intermediate and inner masts. Short distances A and C should beselected and this is constant, so that durability of such mast guiderollers and the bearing surfaces of the masts will be affected. In viewof the above, for the purpose of improving the durability of the bearingsurfaces of the mast channels and guide rollers, it has heretofore beenproposed to employ a three-stage type mast assembly comprising an innermast, intermediate mast and outer mast, in which the distance betweenadjacent mast channels may be varied according to the amount of overlap(FIGS. 2 and 4). In such an arrangement, however, the foreand-aft momentvaries in proportion to the amount of said overlap, and the distances Aand C between the mast rollers 6 and 7 and 4-5 will vary in proportionto the amount of overlap, so that the durability of the bearing surfacesof the mast rollers 4', 5, 6' and 7 would be improved. However, thespace B between the rearward flange 1B of the outer mast 1 and theforward flange 3A of the inner mast 3 will be increased, so that thecenter of gravity will be displaced in a forward direction. Moreover,with an enlargement of said distance B, the position of the lift forkwill also be displaced forwardly from the front end of the truckchassis, and the distance between the center of gravity of the loadmaterials and the center of the front wheel axle of the truck will beincreased, resulting in displacing the center of gravity of the truck,forwardly, thus deteriorating the stability of the truck, and the weightof the balance weight will have to be increased in order to prevent theaforementioned disadvantage. Increase of weight of the said balanceweight will result in increase of its size, and the distance between thefront wheel axle of the truck, and the rear end of the balance weightwill have to be increased accordingly. As a result, the turning radiusof the truck will have to be increased, reducing the maneuverability ofthe truck. With respect to the above-mentioned three-stage mastassembly, the rearward flange 1B of the outer mast l is positioned inthe vicinity of the brake drum 19 on the front wheel axle in order tobring the center of gravity of the mast assembly into the vicinity ofthe truck chassis. In such an arrangement, however, another disadvantagewill occur. Arranging the outer mast l in a position as near as possibleto the drum 19, means that the rearward flange 1B of the outer mast 1 isarranged behind the forward side of the differential gear case 20, andthat the rear side of the lift cylinder 9 can not be arranged in aposition in line with the rear flange 18 of the outer mast 1, even ifthe rear side of the lift cylinder 10 were disposed as near as possibleto said gear case 20. Moreover, the lift cylinder 9 for a three-stagemast assembly has a larger diameter in contradistinction to the liftcylinder for a twostage mast assembly, so that the forward side of saidlift cylinder 9 will have to project beyond the forward flange IA of theouter mast 1. Consequently, during lifting of the fork said cylinder 9would contact with any obstacle such as shelves, so that the cylinder 9would be subject to damage.

Accordingly, an object of the present invention is to provide animproved arrangement of the three-stage mast assembly for a lift truckof the above-mentioned character which is not subject to the foregoingdisadvantages. The new arrangement according to this invention will nowbe described in detail referring to the drawings, FIGS. 5 through 7. Thereference numeral l designates the outer mast with the lower end pivotedto the forward part of the lift truck chassis and adapted to beoscillated fore and aft by means of a tilt cylinder (not shown). 2 is anintermediate mast vertically and telescopically slidable relative tosaid outer mast l, and consists of I- or L-cross section channel. Theforward and rearward flanges 2A and 28 thereof are disposed behind theforward and rearward flanges 1A and 18, respectively of said outer mastl, and nearest to the brake drum l9. 3 is an inner mast consisting of achannel of I- or L-shaped cross section, and is movable in telescopicalmovement along the said intermediate mast 2. Forward and rearwardflanges 3A, 3B are disposed in front of the forward and rearward flanges2A and 2B respectively of the intermediate mast 2, and substantially inline with the forward and rearward flanges 1A 1B of the outer mast l. 4is a guide roller pivotally mounted on the upper part of the outer mastand engaging with the intermediate mast channel 2. 5 is a guide rollerpivotally mounted on the lower part of the intermediate mast 2 andengaging with the outer mast channel 1. Said two rollers 4 and 5 areengaging with the adjacent masts, so that the intermediate mast 2 istelescopically associated with the outer mast 1, and the fore-and-aftmoment of the intermediate mast 2 is transmitted to and the intermediatemast is supported by the outer mast l, as guided by the roller 4. 6 is aguide roller pivotally mounted on the upper part of the intermediatemast 2 and engaging with the inner mast 3. 7 is a guide roller pivotallymounted on the lower part of the inner mast 3 and engaging with theintermediate mast 2. Said two rollers 6 and 7 are in engagement with theadjacent masts, and the foreand-aft moment of the inner mast 2 istransmitted to and the inner mast is supported by the intermediate mast2. 9 is a lift cylinder mounted in a position near the differential gearcasing 20, from which extends the piston rods 10 and 11. The upper endof the uppermost piston rod I1 is associated with the upper end of theinner mast 3. I2 is an engagement member on the lower end of the innermast 3, and 13 is another engagement member or a supporter on theintermediate mast 2, adapted to transmit the lifting motion of the innermast and to support said inner mast in the desired position. 8 is a liftbracket adapted for vertical movement by the engagement of the liftroller 21 with the inner mast 3.

The three-stage mast assembly according to the invention being arrangedin the manner substantially as described and illustrated, it will beseen that when the piston rods 10 and 11 are extended by operating thelift cylinder 9, the inner mast 3 will be elevated. When the mast 3reaches the predetermined position, the engaging element 12 will engageswith the engaging element 13 of the intermediate mast 2, finishingthereby the first stage elevating operation. By continued operation ofthe lift cylinder 9, the said piston rod 1 1 will be extended, so thatthe intermediate mast 2 will be elevated, being pulled by the inner mast3.

From the foregoing, it will be understood that the characterizingfeature of the present invention resides in the fact that theintermediate mast channel 2 of I- or L-shaped cross section is arrangedwith its forward and rearward flanges 2A and 28 arranged rearwardly fromthe forward and rearward flanges 1A 1B and 3A 3B, respectively, of theouter mast 1 and of the inner mast 3, as shown in H0. 6, all masts beingso arranged that the forward and rearward flanges 3A and 3B of the innermast 3 are positioned substantially in line with the forward andrearward flanges 1A 1B of the outer mast 1. In the prior arrangement ofa three-stage mast assembly, the front part of the lift cylinder 9 willhave to be disposed forwardly from the forward flange 1A of the outermast 1. In contradistinction to the above, according to the presentinvention, the forward flange 1A of the outer mast 1 can be placedforwardly from the forward flange 2A of the intermediate mast 2 which isnearest to the truck chassis in the vicinity of the brake drum 19, sothat the forward flange 1A of the outer mast 1 may be disposed forwardlyof the front part of the lift cylinder 9. Consequently, said rearwardflange 1A serves to protect the lift cylinder 9, thus removing thedisadvantage of damage to the lift cylinder liable to occur due to theinterference thereof with shelves provided in a low position.

Moreover, the distance B (FIG. 6) between the forward flanges 3A and 1A,respectively, of the masts 3, 1 and the rearward flange 2B of theintermediate mast 2 is shorter than the corresponding distance B in caseof the prior art arrangement of the mast assembly (FIG. 4). As a resultof such improvement, the center of gravity of the mast assembly isdisplaced to a position rearwardly from the center of the outer mast 1,viz.

nearer to the truck chassis. Consequently, the distance between thecenter of gravity of the load materials on the lift fork and the centerof the front wheel axle of the lift truck is shortened. The center ofgravity of the truck per se remains on the rear side of the truck,resulting in an increase of the stability of the truck, minimizing thesize of the required balance weight as well as minimizing the distancebetween the front wheel axle and the rear end of the chassis, wherebythe turning radius of the truck can be minimized.

According to the present invention, as will be seen from the foregoing,the forward and rearward flanges 2A and 2B of the intermediate mast arearranged rearwardly from the forward and rearward flanges 1A and 1B and3A and 38, respectively, of the outer and inner masts, thereby attainingthe advantageous result for to the mast assembly consisting of channelsof lor L-shaped cross section.

I claim:

1. In a three-stage mast assembly for a lift truck having a pair ofouter mast channels, a pair of intermediate mast channels between andtelescopically associated with said outer mast channels respectively,and a pair of inner mast channels between and telescopically associatedwith said intermediate mast channels respectively, each of said mastchannels having opposed forward and rearward, with respect to the truck,flanges, the distance between said flanges being equal on all channels;the improvement wherein said forward and rearward flanges of each saidintermediate mast channel are positioned rearwardly of said forward andrearward flanges each said outer mast channel respectively, and saidforward and rearward flanges of each said inner mast channel arearranged forwardly of said forward and rearward flanges of each said intermediate mast channel.

2. The improvement as claimed in claim I wherein said forwardand-rearward flanges on said outer mast channels are aligned, in thedirection between the channels of the pairs of channels, with theflanges or said ipne; mast channels.

1. In a three-stage mast assembly for a lift truck having a pair ofouter mast channels, a pair of intermediate mast channels between andtelescopically associated with said outer mast channels respectively,and a pair of inner mast channels between and telescopically associatedwith said intermediate mast channels respectively, each of said mastchannels having opposed forward and rearward, with respect to the truck,flanges, the distance between said flanges being equal on all channels;the improvement wherein said forward and rearward flanges of each saidintermediate mast channel are positioned rearwardly of said forward andrearward flanges each said outer mast channel respectively, and saidforward and rearward flanges of each said inner mast channel arearranged forwardly of said forward and rearward flanges of each saidintermediate mast channel.
 2. The improvement as claimed in claim 1wherein said forward and rearward flanges on said outer mast channelsare aligned, in the direction between the channels of the pairs ofchannels, with the flanges on said inner mast channels.